Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations are all false (not read-only, not idempotent, not destructive), so the description must carry the burden of behavioral disclosure. It mentions 'max 20 queries/session' as a constraint, but does not state that this operation deducts funds from the session balance, that it requires a valid open and funded session, or that it returns query results. The description's 'Buy per-query access' hints at payment but does not explicitly describe the side effects. It does not contradict annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is short and structured with pricing and sequence. It is not overly verbose, but it packs multiple pieces of information (pricing, listing, max queries, sequence) into one sentence without clear separation. The key action is buried. It is not front-loaded with the most critical information (that this executes a query). Adequate but not optimal.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the complexity (5 parameters, no output schema), the description is incomplete. It does not explain the required session_id, the query content constraints, the meaning of k or delivery_receipt, or what the response looks like. It mentions the sequence and a pricing limit, but misses many prerequisites and expectations. An agent would need to inspect the schema or other tools to understand how to call this correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The description provides zero parameter-specific information. The schema already describes session_id and sandbox_receipt, but k, query, and delivery_receipt remain undocumented in both schema and description (schema coverage only 40%). The description does not compensate for the missing parameters, nor does it explain how query or k affect the call. This is a significant gap.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description focuses on the pricing and sequence rather than the core action. 'Buy per-query access' is ambiguous — it does not explicitly state that this tool runs a query against an existing funded session. The actual purpose (execute a prepaid query) is only implied by the sequence and the schema description, not the tool description. It does not clearly differentiate from data_preview beyond the paid aspect.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides a sequence (data_session_open → data_session_fund → data_session_query) which implies when to use this tool (after funding). It also mentions data_preview as a free alternative. However, it does not explicitly state when NOT to use this tool, nor does it explain the trade-offs with other siblings like data_session_attach_escrow. The guidance is implicit rather than explicit.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.